Water heater control system



June 5, 1945. c. M. osTERHl-:LD 2,377,441

WATER HEATER CONTROL SYSTEM Filed March 20,- 1944 l INVENTOR. CLARK/7 OSTEPf/El) A Traa/ffy Patented June 5, 1945 WATER HEATER coNTnoL SYSTEM Clark M. Osterheld, Stoughton. Wis.. signor to McGraw Electric Company, Elgin, lll., a oorporation of Delaware Application March 20, 1944, Serial No. 527,301

(Cl. 21H9) 4 Claims.

My invention relates to electric heating and particularly to control systems for hot water tank heaters.

An object of my invention is to provide a system for controlling the electric heater of a domestic hot water tank adapted to be energized during night hours to ensure that all' oi' the water in the tank shall be hot bei'ore the heater is deenergized.

Another object of my invention is to provide a heater control system adapted to energize an electric heater during night hours only and that shall ensure continuation of energization of the heater beyond the night hours in case less than all of the water in the tank is hot when daylight comes on.

Other objects of my invention will either be apparent from a description of one form of control system embodyingmy invention or will be pointed out in the course of such description and set forth `particularly in the appended claims.

In the `drawing,

Figure l is a view in vertical section through a domestic hot water tank having associated therewith a control system embodying my invention,

Fig. 2 is a diagram of connections embodying my invention, and,

Fig. 3 is a fragmentary diagram of connections showing somewhat diilerent parts.

Referring to Fig. 1 of the drawing, I have there illustrated a usual domestic hot water tank il having a lower cold water inlet pipe I3, an upper hot water outlet pipe it, heat-insulating material Il around the tank, which latter may be held in proper operative position relative to the tank l I by an outer casing I9. y

I provide preferably, but not necessarily, a single electric heater 2 l, which, if only a. single electric heater is used, is located near the lower end of the tank. I have illustrated a clamp-on electric heater preferably located in a, tunnel 23. All of these hereinabove described parts are old and well known in the art and constitute no part of my present invention.

Referring now to Fig. 2 of the drawing, I have there illustrated one diagram of connections embodying my invention as used to control the electric heater 2i. I provide a lower main thermally-actuable heater control switch 25 which is illustrated generally or schematically only as comprising a bimetal bar 21, having one end thereof xed on a contact member 29, while the other free end thereof is adapted to be engaged with and disengaged from a second ilxed contact member I l to which one end of the electric heater 2| is connected.

I provide also a thermal retarder designated as an entity by numeral 33 and which is disclosed and claimed in my co-pending application, S. N. 511,387, illed November 22, 1943, and assigned to the same assignee as is the present application.

-This thermal retarder includes'a heat-conduct-v ing support 35, which is preferably secured to the outside of the tank li at substantially the midheight thereof. It includes further a high expension rod 31, mounted on the support 25, and a low expansion rod 39, supported by supporting member 35 with a block Il of Iheat-insulating material disposed therebetween to render the now of heat from heat-conducting support 3l to low expansion member 39, as small as possible. The thermal retarder 33 includes further a switch contact arm 43, which is of substantially L-shape and is supported at -two points thereof by rods Il and I9. The switch contact part of member 43 is adapted to engage with and be disengaged from two fixed contact members 45 and When the support 35 is subject to the temperature of cold 'water in the tank, that is either when the tank is iirst iilled with cold water, or becomes lled with cold water .during normal operation thereof, the length of expansion rod 31 will be a minimum. By cold water I mean water which has a temperature on the order of to 70 F., or slightly less. When the length of expansion rod 3l is a minimum and the temperature oi' the low expansion rod Il is that oi' the ordinary room, on the order oi F., the switch member portion of member 43 will be in engagement with contact members l5 and 4l. If now, because of energization of heater 2| for a length oi' time suiiicient to cause the temperature of the water in the tank to approach a predetermined maximum value on the order of F., the temperature of rod l1 will also be on the order of 150 F. with the result that, if expansion rod 29 is still at ordinary room temperature, or only slightly thereabove, the bridging 'member I2 will be disengaged from contact members 45 and Il.

I provide further a low wattage heating coil It operatively associated with the low expansion rod I9, which heating' coil, when energized for a length oi' time on the order oi' four to six hours,

will cause an increase in the temperature of rod 39 to a value on the order oi' 300 F. and resultant expansion longitudinally oi' rod 38. with the result that even though expansion rod 31 is heated because of being subject to hot water in the tank, the position of switch arm Il will be again in engagement with contacts l and l1, In order to vary the length of time required for heating coil 4I, when energized, to cause temperature rise of expansion rod 38 to a value on the order of 300 F., I may provide an adjustable rheostat l I, which may be adJusted as may be found desirable or necessary.

I provide a light-sensitive device Il, shown in Fig. 2 as being a selenium cell, which cell has the property of being non-conducting when dark and being conducting when subject to daylight or other artificial light. I am particularly interested in so arranging cell 53 that it is subject to daylight.

An electromagnetic heater control switch l5 is controlled by cell 53 and includes an upper electromagnetic core 51, a lower electromagnetic core 59, and a contact bridging member 8| carried and movable with the two cores 51 and 59. The upper core 51 is provided with a coil 63, which is adapted to be traversed by a coil passing through selenium cell 53 during daylight hours. Contact bridging member 6| is adapted to be engaged with and disengaged from a pair of ilxed contact members 61 and 69. I provide a pair of supply circuit conductors 1| and 13, one terminal of cell 53 being connected to the first supply circuit conductor 1|, while the other terminal of cell 53 is connected to one terminal of coil 63, the other terminal of coil 63 being connected by a conductor 15 to the second supply circuit conductor 13. The second supply circuit conductor 13 is connected by a conductor 11 to fixed contact 29 of the thermallyactuable switch 25. The other terminal of heater 2| is connected by a conductor 19 to contact 41. The second contact 3| of heater control switch 25 is connected, as has already been stated, to one terminal of heater 2| and by a conductor 8| to one terminal of the adjustable rheostat 5|, while the other terminal of rheostat 5| is connected bya conductor 83 with one terminal of heating coil 49, the other terminal of which is connected by a conductor 85 to contact 45.

The lower electromagnetic armature core 59 is provided with a coil 81, one terminal of which is connected by a conductor 89 to contact 45, while the other terminal of coil 81 is connected by a conductor 9| with fixed Contact 61 of the electromagnetic switch 55. The other contact 68 is connected by a conductor 93 with the ilrst supply circuit conductor 1|. It may here be pointed out that coil 63 is a coil of relatively fine wire having a relatively large number of turns in order to provide the necessary effect upon electromagnetic armature core 51, when traversed by a current ilowing through cell 53, namely to cause disengagement between contact bridging member 6| and the ilxed contacts 61 and 59. Coil 81 is made of relatively heavy wire, since it is adapted to be traversed by the current flowing through heater 2|.

It is evident that with the location of cell 53 such that it will be subject to daylight, current will flow through cell 53 shortly after sunrise, with the result of raising of the two armature cores 51 and 59 to cause disengagement of contact bridging member 6i from the fixed contacts 61 and 69. The heater circuit will therefore be opened, particularly so if substantially all of the water in the tank was heated during the hours of darkness, so that bimetal bar 21 was moved away from engagement with fixed contact 3| before daybreak.

If, however, because of demand for and use of hot water during late night hours, with the result that cold water entered the tank, say to a point above the position ci the thermal retarder I8, with the result that the thermal retarder was subiect to cold water with attendant engagement of switch member Il with contacts 45 and 41, energization o! heater 2l would have been eiIected, since bimetal bar 21 would also be subject to cold water. The circuit of heater 2| will be traceable substantially as iollows: from supply circuit conductor 'Il through conductor 11, main thermal switch 25, heater 2|, conductor 18, through closed switch of the thermal retarder 33, that is contact l1, switch arm 4I, contact 4l, conductor 8l and coil 81, conductor 0|, contacts 81 and 6I, and bridging member 5|, and through conductor Il to the other supply circuit conductor 1I. This is made possible by reason of the fact that cell 5I, being in darkness, will be non-conducting so that normally contact bridging member 6I will be in engaged position relatively to contacts 61 and Il. It has already been assumed that a relatively large amount of cold water is in tank ii, and this amount is so great that all of the water in the tank will not be hot by daybreak. The design of coil 81 is such that it will overcome the tendency of coil 63, traversed by current flowing through cell 53 after daybreak, to raise the Contact bridging member 6| upwardly and out of engagement with contacts 81 and 68 and will keep contact bridging member 6| in engagement with contacts 61 and 69, the result being that energization of heater 2| will continue until substantially all of the water in the tank is hot, when main thermal switch 25 will open the circuit.

Let it be assumed that the amount of cold water in tank is not as great as in the above example and that the bimetal bar 21 was moved into engagement with contact 3| at a time, say on the order of five hours, before daybreak. Closure oi the main thermal switch 25 would cause energization of heating coil 49, with the result that the temperature of the low expansion member 39 would be raised to a value on the order of 300 F., just before daybreak, with the result that the thermal retarder heater control switch would be moved to closed position to establish the hereinbefore mentioned energizing support for heater 2|, with the result that even though cell 53 would beV traversed by a current after daybreak, the electromagnetic switch 55 would not be moved to open position until substantially all of the water in the tank was heated to a predetermined high temperature, when switch 25 would be moved to open position to deenergize the system.

It is obvious that with opening of the electromagnetic switch 55, when substantially all of the water in the tank has been heated to a predetermined high temperature, the contact bridging member 6| would be moved upwardly out of engagement with its cooperating contacts so that the entire control system would be deenergized for the rest of the daylight hours.

Referring now to Fig. 3, I have there illustrated a modification of my control system in which a photo-electric cell or bulb is used, this bulb being of the kind adapted to generate an electric current when subjected to daylight. The coil 63 is connected to the terminals of bulb 95 and is adapted to be positioned around the upper end of an elongated electromagnetic armature core 91. The core 91 is adapted to actuate a contact bridging member 99 into and out of engagement with fixed contact -members |0| and |03. Contact member |03 is connected to supply circuit conductor 1| as by a conductor 93. Contact |0| is connected by a conductor |05 to onel v provided with a heating coil, the'energization of terminal of coil 81 positioned around the lower end of core 91, the other end of coil 81 being connected by a. conductor |01 with contact member 45 of the thermal retarder switch 33.

It will be evident that the operation of the control system, part of which is shownin Fig. 3. to replace like parts in the system shown in Fig. 2, will be substantially the same as that set forth in the description of Fig. 2.

I may point out also that while I have shown a direct connection between the selenium cell 53 and coil 63, it is within the province of my invention to interpose a relay designed to control a secondary circuit, including coil 63, and the same remarks apply as to the diagram of connections shown in Fig. 3.

It is the rule in some utilities supplying electric energy for light, heat, and power, to require that water heaters be disconnected `from their circuits during daylight hours, Aand this makes it desirable, even necessary, to ensure that those few installations of electric water'heaters which experience extra heavy demands for hot water during late night hours shall be controlled so that the tank is full of hot water before the heater is ilnally disconnected from the supply circuit. It is obvious further that the control systems shown in Figs. 2 and `3 of the drawing will accomplish such object and that they employ a minimum number of component and cooperative elements in attaining such object.

Various modifications may be made in the system embodying my invention without departing from the spirit and scope thereof, and all such modiilcations coming clearly within the scope of the appended claims are to be considered a part of my invention.

I claim as my invention:

1. A water heater control system for a hot water tank having an electric heater, said system comprising a rst thermal heater control switch subject to tank water temperature at the lower end of the tank, a thermal retarder switch unit mounted on the tank intermediate the ends thereof and including a ilrst expansion member subject to tank water temperature. a. second expansion member out of close thermal communication with said tank, a `heating coil for said second expansion member and a second heater control switch connected in series circuit with said rst heater control switch, a third heater control switch connected in series circuit with said other two heater control switches, a light sensitive means effective to hold said third heater control switch in open position during daylight hours and means to cause prolongation of the energization ot the lheater beyond the start oi' daylight hours in case less than all of the water in the tank is hot at that time, said means comprising heater-current controlled means for holding said third heater control switch in closed position until deenergization of the heater by said iirst thermal heater control switch.

2f. A water heater control system for a hot water tank having an electric heater, said system comprising a ilrst thermal heater control switch enective'to deenergize said heater when substantially all of the water in the tank is hot, ay

second daylight-controlled heater control switch elective to deenergize said heater when daylight starts, a thermal retarder switch unit comprismg a pair of expansion members, one oi which is subject to tank water temperature intermediate the ends of the tank and the second ol which is which is controlled by said iirst and second switches and a third heater control switch in series circuit with said other two switches, said thermal retarder switch unit being effective to cause closure of its switch and energization of said heater with a preset time period of delay after start of darkness in case of use of only a relatively small amount of hot water from the tank and means to cause prolongation of the energization or' saicll heater beyond tne start of daylight hours in case less than all 0i' the water in the tank is hot at that time, said means comprising heater-current controlled means ior holding said second heater switch in closed position until deenergization of said heater by said first thermal heater control switch.

3. A water heater control system for a hot water tank having an electric heater, said system comprising a rst thermal heater control switch on the tank subject to tank water temperature at the lower end thereof eiiective to deenergize said heater when substantially all of the water in the tank is hot, a second daylight-controlled heater control switch including a coil adapted to carry current during daylight hours to hold said second switch in open position and a heater-current carrying coil on said second switch adapted to hold it in closed position after start or daylight hours in case energization of said heater during night hours has heated less than all of the water in the tank before the start of daylight hours, said ilrst switch being eiective to cause deenergization of the heater when substantially all o! the water in the tank is hot.

4. A water heater control system for a hot water tank having an electric heater, said system comprising a rst thermal heater control switch on the tank subject to tank water temperature at the lower endv thereof effective to deenergize said -heater when substantially all of the water in the tank is hot, a second' heater-control switch oi the electromagnetic type in series circuit with said hrst switch and including a coil, a lightsensitive device for causing said coil to be traversed by a current-during daylight hours to hold the switch in open position to deenergize said heater during daylight hours, a third heater control switch unit in series circuit with said heater and said first and second heater-control switches and including a iirst thermally-expansible member subject to tank water temperature at a portion intermediate the ends thereof, a second thermally-expansible member out oi close thermal communication with the tank water temperature.

ya heating coil for said second thermally-expansible member controlled jointly by said iirst and second heater control switches, said third heater control switch being adapted to be closed immediately after nightfall in case the tank contains enough cold water to aii'ect said nrst thermally-expansible member and to be closed with an adjustably preset time period of delay alter nightfall in case the tank contains only enough cold water to aiiect said ilrst heater control switch and a heater-current traversed coil on said second heater control switch adapted to hold said second switch in closed position after start or daylight hours in case less than all of the water in the tank is hot at the start of daylight hours, said rst thermal heater control switch eiecting deenergization ot tne heater when substantially all o! the water in the tank is hot.

CLARK M. OSTERHELD. 

